Optical recording medium for short-wavelength of laser beam and read/write/erase method using the medium

Abstract

An optical recording medium of a data rewritable type includes: a substrate; a first transparent dielectric layer formed on the substrate, having a refractive index substantially equal to the refractive index of said substrate; a second transparent dielectric layer formed on the first dielectric layer, having a refractive index greater than that of said first dielectric layer and having its thickness being not greater than 80 nm; and further includes an optical recording layer formed on the second dielectric layer, so that said first and second dielectric layers and optical recording layer are laminated in this order on said substrate, where the total film thickness of the first and second dielectric layers is set to be not smaller than 90 nm.

What is claimed is: 
     
       1. A data rewritable optical recording medium on which reading/writing of data is executed by applying a laser beam thereto, said optical recording medium comprising: a substrate;   a first transparent dielectric layer formed on said substrate, having a refractive index in a range of not smaller than 1.4 and not greater than 1.7;   a second transparent dielectric layer formed on said first dielectric layer, having a refractive index greater than that of said first dielectric layer and having its thickness being not greater than 80 nm wherein its thickness is set in a range of not smaller than λ/6.4 n and not greater than λ/3.9 n, where λ represents the wavelength of the laser beam and n represents the refractive index of said second dielectric layer;   an optical recording layer formed on said second dielectric layer, so that said first and second dielectric layers and optical recording layer are laminated in this order on said substrate,   wherein the total film thickness of said first and second dielectric layers is not smaller than 90 nm.   
     
     
       2. The optical recording medium as claimed in claim 1, wherein said first dielectric layer is comprised of a material having a composition of (MgO) x  (SiO 2 ) 1-x , where 0≦×≦0.67. 
     
     
       3. The optical recording medium as claimed in claim 1, wherein said substrate is made of a plastic material, and said first dielectric layer is comprised of any one of compounds in a group consisting of SiO 2 , MgO, and BeO, and a mixture of one of MgO, BeO, Al 2  O 3  and silicon oxide (SiO 2 ), while said second dielectric layer is comprised of any one of compounds in a group consisting of silicon nitride (Si 3  N 4 ), aluminum nitride, zinc sulfide (ZnS), zinc selenic (ZnSe), selenium sulfide, tantalum oxide (Ta 2  O 5 ), and a mixture of any of the materials and silicon oxide (SiO 2 ). 
     
     
       4. The optical recording medium as claimed in claim 1, wherein said substrate has a tracking guide groove formed thereon. 
     
     
       5. The optical recording medium as claimed in claim 4, wherein a track pitch thereof is not greater than 1.3 μm. 
     
     
       6. The optical recording medium as claimed in claim 4, wherein write/erase of data is effected on a plurality of continuous tracks by applying a laser beam having a wavelength being not greater than 680 nm. 
     
     
       7. The optical recording medium as claimed in claim 6, further comprising an identification mark disposed on one of the recording medium and a cartridge case containing the recording medium, said identification mark for determining whether or not the recording medium satisfies the condition that when the write/erase of data is continuously effected on the tracks, radial acceleration is prevented from increasing at the time of switching incident power. 
     
     
       8. The optical recording medium as claimed in claim 7, wherein judgment whether the writing/erasing operation is effected or prohibited is based on whether said identification mark is provided or not.